The present invention relates generally to valves and more particularly to an improved positive pullback synchro valve actuator for use on a wide variety of different types of valves.
In the prior art, it has been necessary to adjust the relative proportions of air vis-a-vis gas or oil for purposes of providing a proper mixture for combustion. In determining the proper mixture for combustion and controlling the same, certain non-linear adjustments have been necessary with regard to either one or both of the fluids which form the mixture.
In the prior art, it has also been difficult to achieve proper proportioning of fluids mixed for combustion in a proportioning apparatus. Also, apparatus for such proportioning of fluids in the prior art have been expensive and/or difficult to produce in accurate embodiments.
Further, in the prior art, various compensations in the proportioning of the air-fuel ratio have been necessary due to variables which occur in the firing operation. Such factors include change in the pressure at which fuel or air is supplied to the proportioning device, and which will tend to be slightly reduced as the firing rate increases. This is true both with respect to the combustion air and the fuel supply. Also, changes in the interior frictional resistance of the air or fuel piping as caused by the increase or decrease of the rate of flow of fluids therethrough are also factors. Yet further, changes in internal furnace pressure such as are caused by an increase or decrease in the firing rate of the burners must be compensated for.
The prior art has found it difficult to accomplish all of the above necessary factors in a mechanically efficient and cost efficient manner. As a partial solution to these problems, valve actuators including universal cam strip assemblies have been suggested. However, prior art valves which have utilized adjustable cam strips have had the deficiency of not being able to provide assurance that the valve was closed when the cam assembly was rotated by the operator.
Accordingly, it is a principal object of the improved positive pullback synchro valve actuator of the present invention to materially reduce the difficulties and disadvantages of the prior art devices.